Tubular prostheses including tubular stents, grafts, and stent-grafts (e.g., stents having an inner and/or outer covering comprising a layer of graft material and which may be referred to as covered stents) have been used to treat vascular disorders such as stenoses and aneurysms.
A stenosis involves the narrowing of a duct or canal such as a blood vessel where it generally impedes blood flow. Stenoses have been treated using self-expanding or balloon expandable tubular prostheses (e.g., a balloon expandable device), which are positioned within the stenotic portion of a blood vessel, for example, to maintain lumen integrity after the vessel has been widened or to widen the vessel to improve or restore desirable blood flow therethrough.
In contrast, an aneurysm involves abnormal widening of a duct or canal such as a blood vessel and generally appears in the form of a sac formed by the abnormal dilation of the duct or vessel wall. The abnormally dilated wall typically is weakened and susceptible to rupture. Aneurysms can occur in any blood vessel including the abdominal aorta. Rupture of an abdominal aortic aneurysm, which is below the renal arteries and extends distally to or toward the iliac arteries, can be fatal. Tubular prostheses including grafts and stent-grafts have been used to treat aneurysms. They are generally placed to extend through the aneurysmal sac and beyond the proximal and distal ends thereof to replace or bypass the dilated wall. When used in blood vessels, the tubular wall of the prosthesis is designed to prevent blood flow therethrough so that the blood bypasses aneurysmal sac. The prostheses described above can be implanted in an open surgical procedure (grafts) or placed endovascularly (stent grafts).
In open vascular surgery, the space around the diseased vessel is surgically opened, the vessel is opened, and the graft ends are sutured into position inside of or as a substitute for the diseased vessel. In contrast, the endovascular or minimally invasive approach typically involves providing a delivery catheter loaded with a radially compressed or folded prosthesis, delivering the catheter and prosthesis into the vasculature (e.g., into a femoral artery), and delivering the prosthesis endovascularly to the aneurysm location. The prosthesis is deployed at the target site where it is either expanded through the use of a balloon or a radial restraint is removed to allow the device to radially expand if it is a self-expanding device. For example, if the prosthesis is a self-expanding stent graft, the stent graft radially expands from its compressed configuration to its expanded configuration upon release of a restraint (e.g., a sheath or the inner wall of the delivery catheter) that maintains the stent graft in its low profile compressed configuration for delivery through the vasculature.
Although the endoluminal approach is much less invasive, and usually requires less recovery time and involves less risk of complication as compared to open surgery, methods of improving fixation and reducing migration continue to be of interest. The outward spring force of a self-expanding stent-graft if not sized and positioned with an adequate interface pressure may not be sufficient to prevent migration. This problem can be exacerbated when the vessel's fixation zone is not round or is calcified. Migration can result in leakage of blood around the prosthesis and into the aneurysmal sac, which, in turn, may increase the chance of rupture of the dilated vessel wall. When there is a short landing zone between the aortic aneurysm and a proximal branching artery (e.g., the renal arteries, carotid or brachiocephalic artery) small deviations in sizing and placement may result in migration and/or leakage.
Radially extending members such as tines, barbs, hooks and the like that engage the vessel wall, are used in some devices to minimize migration.
One method has been to simply inject a filler substance, such as foam, into the aneurysmal sac after the stent-graft has been placed in the desired location
Other approaches using such substances have been to incorporate a substance onto a stent-graft such as cat gut cellulose and nylon, see U.S. Pat. No. 6,165,214. These approaches, however, have limitations. The incorporation of the substance into the stent-graft approach is limited in the amount of the substance that can be incorporated into the device and then delivered. And an approach where a substance is simply injected at the proximal neck does not provide for containment of the substance. As a result, the substance can flow away from the neck, thereby reducing its effectiveness.
There remains a need to develop and/or improve seal and/or fixation approaches for endoluminal or endovascular prostheses placement.